added Registry::entity

TODO

@@ -6,8 +6,8 @@
 * define systems as composable mixins (initializazion, reactive, update, whatever) with flexible auto-detected arguments (registry, views, etc)
 * create dedicated flat map based on types implementation (sort of "type map") for types to use within the registry and so on...
 * registry::create with a "hint" on the entity identifier to use, it should ease combining multiple registries
-* add a member function aside current and version to get the actual identifier without its version
 * can we do more for shared libraries? who knows... see #144
+* filtered views (has, hasn't and so on)
 * work stealing job system (see #100)
 * reflection system (maybe)
 * C++17. That's all.

src/entt/entity/registry.hpp

@@ -387,10 +387,19 @@ public:
         return (entities[pos] == entity);
     }
 
+    /**
+     * @brief Returns the entity identifier without the version.
+     * @param entity An entity identifier, either valid or not.
+     * @return The entity identifier without the version.
+     */
+    entity_type entity(const entity_type entity) const ENTT_NOEXCEPT {
+        return entity & traits_type::entity_mask;
+    }
+
     /**
      * @brief Returns the version stored along with an entity identifier.
      * @param entity An entity identifier, either valid or not.
-     * @return Version stored along with the given entity identifier.
+     * @return The version stored along with the given entity identifier.
      */
     version_type version(const entity_type entity) const ENTT_NOEXCEPT {
         return version_type((entity >> traits_type::entity_shift) & traits_type::version_mask);
@@ -442,7 +451,6 @@ public:
         if(available) {
             const auto entt = next;
             const auto version = entities[entt] & (~traits_type::entity_mask);
-
             entity = entt | version;
             next = entities[entt] & traits_type::entity_mask;
             entities[entt] = entity;
@@ -524,10 +532,10 @@ public:
         // just a way to protect users from listeners that attach components
         assert(orphan(entity));
 
+        // lengthens the implicit list of destroyed entities
         const auto entt = entity & traits_type::entity_mask;
         const auto version = (((entity >> traits_type::entity_shift) + 1) & traits_type::version_mask) << traits_type::entity_shift;
         const auto node = (available ? next : ((entt + 1) & traits_type::entity_mask)) | version;
-
         entities[entt] = node;
         next = entt;
         ++available;

test/entt/entity/registry.cpp

@@ -198,6 +198,22 @@ TEST(DefaultRegistry, Functionalities) {
     ASSERT_TRUE(registry.empty<int>());
 }
 
+TEST(DefaultRegistry, Identifiers) {
+    entt::DefaultRegistry registry;
+    const auto pre = registry.create();
+
+    ASSERT_EQ(pre, registry.entity(pre));
+
+    registry.destroy(pre);
+    const auto post = registry.create();
+
+    ASSERT_NE(pre, post);
+    ASSERT_EQ(registry.entity(pre), registry.entity(post));
+    ASSERT_NE(registry.version(pre), registry.version(post));
+    ASSERT_NE(registry.version(pre), registry.current(pre));
+    ASSERT_EQ(registry.version(post), registry.current(post));
+}
+
 TEST(DefaultRegistry, RawData) {
     entt::DefaultRegistry registry;
     const entt::DefaultRegistry &cregistry = registry;